DNA Damage Induced by Temozolomide Signals to both ATM and ATR: Role of the Mismatch Repair System

• Published in: Molecular pharmacology Vol. 66; no. 3; pp. 478 - 491
• Main Authors: Caporali, Simona, Falcinelli, Sabrina, Starace, Giuseppe, Russo, Maria Teresa, Bonmassar, Enzo, Jiricny, Josef, D'Atri, Stefania
• Format: Journal Article
• Language: English
• Published: United States American Society for Pharmacology and Experimental Therapeutics 01.09.2004
• Subjects: Antineoplastic Agents, Alkylating - pharmacology; Apoptosis; Ataxia Telangiectasia Mutated Proteins; Base Pair Mismatch; Cell Cycle - drug effects; Cell Cycle Proteins - metabolism; Cell Division - drug effects; Checkpoint Kinase 1; Checkpoint Kinase 2; Dacarbazine - analogs & derivatives; Dacarbazine - pharmacology; DNA Damage - drug effects; DNA Repair - drug effects; DNA-Binding Proteins; Humans; Phosphorylation - drug effects; Protein Kinases - metabolism; Protein-Serine-Threonine Kinases - metabolism; Serine - metabolism; Time Factors; Tumor Cells, Cultured; Tumor Suppressor Protein p53 - metabolism; Tumor Suppressor Proteins
• ISSN: 0026-895X; 1521-0111

The mammalian mismatch repair (MMR) system has been implicated in activation of the G 2 checkpoint induced by methylating agents. In an attempt to identify the signaling events accompanying this phenomenon, we studied the response of MMR-proficient and -deficient cells to treatment with the methylating agent temozolomide (TMZ). At low TMZ concentrations, MMR-proficient cells were growth-inhibited, arrested in G 2 /M, and proceeded to apoptosis after the second post-treatment cell cycle. These events were accompanied by activation of the ATM and ATR kinases, and phosphorylation of Chk1, Chk2, and p53. ATM was activated later than ATR and was dispensable for phosphorylation of Chk1, Chk2, and p53 on Ser15 and for triggering of the G 2 /M arrest. However, it conferred protection against cell growth inhibition induced by TMZ. ATR was activated earlier than ATM and was required for an efficient phosphorylation of Chk1 and p53 on Ser15. Moreover, abrogation of ATR function attenuated the TMZ-induced G 2 /M arrest and increased drug-induced cytotoxicity. Treatment of MMR-deficient cells with low TMZ concentrations failed to activate ATM and ATR and to cause phosphorylation of Chk1, Chk2, and p53, as well as G 2 /M arrest and apoptosis. However, all these events occurred in MMR-deficient cells exposed to high TMZ concentrations, albeit with faster kinetics. These results demonstrate that TMZ treatment activates ATM- and ATR-dependent signaling pathways and that this process is absolutely dependent on functional MMR only at low drug concentrations.